As a previous method to separate and recover steel pipe and coating resin, the technique for which the present applicant was granted patent status in Japan is disclosed in Japanese Patent No.2533465.
The technique according to the above-named Japanese patent has been preferably used for resin-coated steel pipe that consist of pipe having a thickness about 0.8 mm and outer diameter of 25.5–40 mm, and a coating of a thermo-plastic synthetic resin, such as acrylonitrile acryl styrene (AAS) or acrylonitrile butadiene styrene (ABS), of a uniform thickness of about 1 mm fixed on the steel pipe surface with a thin film of adhesive.
The means to separate and recover a steel pipe and coating resin, as described in the above Japanese patent, consists of passing a resin-coated steel pipe through or near a high-frequency induction coil by feed rolls and take-up rolls, and heating the pipe to a temperature no lower than the melting point of the resin.
Further, as stated in Claims 1 and 2 and shown in FIGS. 2 through 5 of the above Japanese patent, the coating resin is scraped off into chips of a certain size by scraping rolls, which are used as a separating mechanism located at a position where the inner layer of coating is melted and the outer layer is in a softened condition after passing the high-frequency induction coil, and which rotate in the feeding direction of the pipe. The scraping rolls are provided with blades that fit the shape of the pipe section (circular in FIGS. 2 and 3; square in FIGS. 4 and 5 of the above Japanese patent) and are arranged at a pitch corresponding to the size of the scraped resin chips.
Further, as stated in Claim 3 and shown in FIG. 6 of the above Japanese patent, the scraping rolls, used as a separating mechanism located at a position where the inner layer of coating is melted and the outer layer is in a softened condition after passing the high-frequency induction coil, are rotated in the direction opposite to the feeding direction of the pipe to scrape off the resin into a set of long strips. Here again, the scraping rolls are provided with blades fitting the shape of the pipe section.
Still further, as stated in Claim 4 and shown in FIG. 7 of the above Japanese patent, coating resin is scraped into long strips by scraping blades used for separating and fixed at a position where the inner layer of coating is melted and the outer layer is in a softened condition after passing the high-frequency induction coil.
In Claims 1, 3 and 4 of the above Japanese patent, steel pipe and resin from a resin-coated steel pipe are separated by scraping and are recovered in a segregated condition. For this purpose, at least one pair of scraping blades, opposing each other, are formed into a shape congruent with the outer periphery of the steel pipe when seen from the direction perpendicular to the axis of the pipe.
In order for each of the blades to scrape coating resin from the resin-coated steel pipe into chips of a certain size (from about 10 mm×10 mm to 10 mm×15 mm) or into a set of long strips, it is important that the patent is practiced in such a manner that the blade tips are fitted tightly on the outer periphery of the pipe during the feeding motion for the pipe. But the fact that the tips of each of the blades are formed into a shape congruent with the outer periphery of the steel pipe and must be fitted tightly on the outer periphery of the pipe during the feeding motion, poses the following problems.
Firstly, small pieces or dust (about 1 mm×1 mm through 1 mm×5 mm in size) of steel cut off from steel pipe are mingled with the scraped off resin. This means that in order to reuse the resin separated and recovered from the steel pipe, an additional process and additional equipment to remove the steel pieces or dust from the recovered resin are required.
Secondly, the tips of the scraping blades come in contact with the melted inner layer of coating resin and, in case the apparatus is run continuously, the tips of the blades generate friction heat and raise temperature to a point higher than desirable as they tightly engage with the outer surface of the steel pipe that is moving in the feeding direction, and thus, part of the resin heated over the melting point and separated from steel pipe will gradually stick to the tips of the blades and accumulate. When the resin thus accumulated gradually reaches a certain amount, it must be removed from around the tips of the blades, which means an interruption of continuous run of the apparatus.
The primary object of the present invention, therefore, is to provide a method and an apparatus to separate and recover steel pipe and coating resin from resin-coated steel pipe that make it possible to separate coating resin from the steel pipe without scraping, and hence, without generating cut off dust of steel pipe, and thereby make it possible to run the apparatus continuously.